FIG. 5 illustrates a double-housing machine tool (machining center) 1 as an example of a compound processing machine. The double-housing machine tool 1 includes left and right columns 2, 2 attached to a bed 4, a cross rail 6 movable vertically (in Z-axis direction) on the columns 2, 2, a saddle 7 movable horizontally (in Y-axis direction) on the cross rail 6, a ram 8 movable in the Z-axis direction on the saddle 7, and a table 5 movable in the front-back direction (in X-axis direction) on the bed 4. Furthermore, the ram 8 has a machining head 10 attached thereto, which includes a spindle unit 20 equipped with a spindle to which a tool can be attached.
When machining a workpiece, the double-housing machine tool 1 moves the table 5, the cross rail 6, the saddle 7, and the ram 8, and the machining head 10 indexes the angular position (rotational position) of the spindle unit 20 in accordance with numerical control based on a preliminarily set program. Accordingly, in the machine tool, the tool can be set at appropriate angles for machining various surfaces of the workpiece so that the workpiece can be cut into complicated shapes.
In order to achieve this, the machining head has the spindle unit 20 and is equipped with an index mechanism within a support head component for the spindle unit 20. The index mechanism is for indexing the angular position of the spindle unit 20. A machining head equipped with a drive motor of a direct-drive type (which will be referred to as a DD motor hereinafter) is known as means for driving the index mechanism. The DD motor includes a motor stator and a motor rotor that are disposed within a housing of the machining head 10, and the rotor is linked with a support shaft that supports the spindle unit (for example, Patent Document 1).
Regarding the support head component (operating head component) included in the machining head disclosed in Patent Document 1, the support head component (first support portion) supports the spindle unit (second support portion) with a pair of support shafts disposed on opposite sides of the spindle unit.
Specifically, the support head component disclosed in Patent Document 1 has the shape of a fork in which a pair of support segments (arms) is disposed on opposite sides of the spindle unit. The support segments have the support shafts rotatably contained therein. Each of the support segments has a built-in DD motor that is linked with the corresponding support shaft. Each DD motor rotates the corresponding support shaft so that the spindle unit is rotated about an axis line of the support shaft, whereby the spindle unit can be indexed to a desired angular position.
Although not discussed in Patent Document 1, a machining head used in a machine tool is generally provided with a bearing for rotatably supporting the support shafts and a clamp mechanism for maintaining the indexed angular position of the spindle unit, which are disposed within the support head component. There are also cases where a rotary joint for supplying machining fluid to the spindle unit is disposed within the support head component. These parts will generically be referred to as elements hereinafter.
In the machining head used in the machine tool described above, there are cases where the spindle unit needs to be detached from the support head component for maintenance purposes, such as adjustment and repair. However, in a typical machining head, there are often cases where the spindle unit cannot be readily detached from the support head component by simply unscrewing screw members that maintain the fixed state between the support shafts and the spindle unit. The following is one of the reasons for such a difficulty in the detachment of the spindle unit.
Specifically, in a support head component of a typical machining head, one of the spindle unit and the pair of support shafts is provided with holes (or recesses), and the other is provided with protrusions that are engageable with the holes. The holes and protrusions are provided for the purpose of facilitating the positioning of the spindle unit relative to the support segments when the spindle unit is being attached to the support segments. The hole-and-protrusion engagement technique is generally applied for the positioning between the support shafts and the spindle unit. Consequently, in a support head component that supports the spindle unit by holding the spindle unit between the pair of support shafts disposed on opposite sides thereof, even if the screw members are unscrewed to release the fixed state between the support shafts and the spindle unit, the spindle unit cannot be detached from the support head component unless at least one of the support shafts is slid or displaced in its axial direction to disengage the support shaft from the spindle unit.
Accordingly, in addition to unscrewing the screw members to release the fixed state between the support shafts and the spindle unit, the process for detaching the spindle unit from the aforementioned support head component requires sliding the at least one support shaft in its axial direction to disengage the support shaft from the spindle unit. This process for sliding the support shaft in its axial direction varies depending on the arrangement of the elements in the support head component, but is generally implemented in a manner such that the plurality of elements contained within the support head component is detached in a certain order starting from the elements located farthest from the spindle unit, thereby bringing the support shaft into the displaceable state, and the support shaft is subsequently slid in its axial direction.
The support head component is usually heavy and large in size. For this reason, the aforementioned process is generally implemented on the machine tool with the support head component remain attached to the machine tool, or in other words, without detaching the support head component from the machine tool. However, performing the aforementioned detachment process of the plurality of elements contained within the housing on the machine tool leads to extremely bad workability in view of, for example, the working space, and the process thus requires a large amount of time as well as putting a large amount of workload on the operator. In addition, the detached elements need to be assembled back into the housing with high precision, which is also very time consuming.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-48135